The invention relates to a brake booster comprising an input element for actuating the brake booster, which input element at its brake pedal-side end has a receiving sleeve for an actuating rod, wherein a spring sleeve is provided, which is disposed at least partially inside the receiving sleeve and has a substantially axially extending spring element, which cooperates with the actuating rod when the latter is brought into a detent position in relation to the input element and which is actuable in a spring-elastic manner in a radially outward direction.
From WO 00/07862, and corresponding U.S. Pat. No. 6,505,539 which is incorporated by reference herein, a conventional brake booster is known. An input element of the brake booster is designed at its brake pedal-side end as a fork provided with a transverse bore. To couple a brake pedal lever to the input element, the brake pedal lever, which is likewise provided with a transverse bore, is introduced into the fork and connected by means of a transverse bolt to the fork. The transverse bolt is then secured to prevent it from accidentally falling out.
From DE 33 07 888 A1, which is incorporated by reference herein, a further brake booster is known. Said brake booster has a load transmission arrangement with an input element, which at its end facing the brake pedal has a sleeve-shaped receiver for an actuating rod, which is actuable by means of the brake pedal. The shell of the sleeve-shaped receiver of the input element is provided with an opening, through which a spring element extends in radial direction. The spring element has two spring portions projecting into the interior of the sleeve-shaped receiver as well as two limbs embracing the radially outer side of the receiver. To couple the actuating rod to the input element, the actuating rod is inserted into the sleeve-shaped receiver until the spring portions projecting into the interior of the sleeve-shaped receiver latch into a peripherally extending groove of the actuating rod.
The free spring end of the spring element opposes axial loading both in and counter to the actuating direction of the brake booster with, in each case, substantially the same spring force. However, while in the event of axial loading of the free end of the spring element in actuating direction a comparatively low spring force is desirable to enable the actuating rod to be brought without a great expenditure of force into the detent position, in the event of axial loading of the free end of the spring element counter to actuating direction, on the other hand, a comparatively high spring force is desirable in order to prevent the actuating rod from being pulled out of the receiving sleeve. The load transmission arrangement according to DE 33 07 888 A1 is incapable of fully meeting said requirements.
From DE 198 43 316 A1, which is incorporated by reference herein, a further load transmission arrangement comprising a plurality of spring elements is known. The load transmission arrangement comprises an input element, which at one of its two ends has a receiving sleeve for an actuating rod. A spring sleeve comprising a plurality of substantially axially extending spring elements is disposed inside the receiving sleeve in such a way that the spring elements, which are actuable in a spring-elastic manner in a radially outward direction, cooperate with the actuating rod when the latter is brought into a detent position in relation to the input element.
For connecting the spring sleeve to the receiving sleeve, the spring sleeve at its end facing the actuating rod has a radially outwardly extending collar, which cooperates in the load transmission direction of the actuating rod with an end of the receiving sleeve facing the actuating rod. To prevent the spring sleeve from detaching from the receiving sleeve when the spring sleeve is loaded by an axial force counter to the load transmission direction of the actuating rod, the spring sleeve in a portion disposed inside the receiving sleeve has a plurality of extensions, which extend in a radially outward direction. Said extensions are supported against a step in the interior of the receiving sleeve so that the spring sleeve does not detach from the receiving sleeve even when loaded with an axial force counter to the load transmission direction of the actuating rod.
To couple the actuating rod to the input element, the actuating rod is inserted into the receiving sleeve until a spherical head of the actuating rod facing the input element has passed the spring elements and the spring elements engage behind the spherical head. The spring elements, which engage behind the spherical head and cooperate counter to the actuating direction of the actuating rod with the spherical head, guarantee that a force introduced counter to actuating direction into the actuating rod is transmitted from the spherical head to the spring elements and from the spring elements to the receiving sleeve connected to the input element. The actuating rod is consequently reliably coupled to the input element not only in actuating direction but also counter to actuating direction.
The drawback of the load transmission element known from DE 198 43 316 A1 is however that the connection of the spring sleeve to the receiving sleeve is complex and hence cost-intensive. This is due above all to the fact that, for connecting the spring sleeve to the receiving sleeve, an undercut has to be disposed in the deepest portion of the receiving sleeve. Said undercut is used to form the step, with which the radially outwardly extending extensions of the spring sleeve cooperate counter to the actuating direction of the actuating rod.
The object of the invention is to provide a brake booster which guarantees an improved and, particularly from a manufacturing point of view, more easily realizable connection of the spring sleeve to the receiving sleeve.
Said object is achieved in a brake booster of the type described initially in that the spring sleeve at its brake pedal-side end has a radially outwardly extending portion, which is fastened by means of a bead of the receiving sleeve to the latter. The bead guarantees that both forces introduced in actuating direction and forces introduced counter to actuating direction into the spring sleeve may be reliably transmitted to the receiving sleeve. The bead is moreover extremely inexpensive to realize.
The radially outwardly extending portion of the spring sleeve preferably takes the form of a circumferential or at least in sections circumferential collar. Such a refinement guarantees particularly reliable transmission of forces, which are introduced into the spring sleeve, to the receiving sleeve.
The spring sleeve may comprise two or more spring elements, which cooperate with the actuating rod and surround the radially outer side of the actuating rod. The individual spring elements are expediently separated from one another by slots extending substantially in axial direction. For adjustment of the restoring forces of the spring elements, said slots may at their ends facing the spring sleeve widen in peripheral direction of the spring sleeve. The wider the slots in peripheral direction, the more the restoring forces of the spring elements decrease. This is due to the fact that the webs, by which the spring elements are connected to the spring sleeve, become progressively thinner. According to a preferred embodiment of the invention, the widened portions of the slots at their ends facing the spring sleeve take the form of circular recesses. The slots consequently open at their ends facing the spring sleeve into circular recesses. By means of the diameter of the circular recesses it is likewise possible to exert an influence upon the restoring forces of the spring elements.
According to a preferred embodiment of the invention, the spring element cooperates, e.g. via its free end which is actuable in a spring-elastic manner in a radially outward direction in relation to the receiving sleeve, with a first oblique face of the actuating rod. Said oblique face advantageously has a radial extension increasing in actuating direction and is preferably flat, i.e. not curved, in axial direction. When the actuating rod from the detent position is then acted upon by a tensile force acting counter to the actuating direction, the tensile force is introduced via said oblique face of the actuating rod axially into the free end of the spring element. The axial force introduced into the spring element is in turn introduced by the latter into the receiving sleeve and/or the input element.
A first oblique face of the actuating rod is preferably disposed so as to be inclined relative to the spring element in such a way that the free end of the spring element in the detent position opens approximately at right angles into the first oblique face. Such an arrangement of first oblique face and spring element achieves the optimum introduction of force from the first oblique face into the spring element.
The actuating rod may have, in actuating direction upstream of the first oblique face, a further, second oblique face which is inclined in such a way that the first and second oblique faces form a notch-like profile. The second oblique face is preferably disposed relative to the spring element in such a way that the spring element in the detent position is at least in sections in surface contact with the second oblique face of the actuating rod. The actuating rod may moreover have, in actuating direction downstream of the first oblique face, a third oblique face with a radial extension decreasing in actuating direction. When the actuating rod is being introduced into the detent position, a cooperation of the third oblique face with the spring element advantageously ensues.
At least one of the oblique faces of the actuating rod is preferably designed as a conical portion. Such a rotationally symmetrical design of the oblique faces is advantageous because it then allows the actuating rod to be introduced in any angular position relative to a longitudinal axis of the actuating rod into the receiving sleeve of the input element.
Two or more spring elements cooperating with the actuating rod may be provided, which together in the form of a hollow cylinder or a portion of a hollow cylinder concentrically surround the radially outer side of the actuating rod. By virtue of a plurality of spring elements, forces may be introduced more uniformly from the spring elements into the actuating rod and/or from the actuating rod into the spring elements.
The spring elements may be formed e.g. as finger-like strips integrally with the e.g. hollow-cylindrical spring sleeve. The spring sleeve preferably extends parallel to the receiving sleeve and lies against the radially inner surface of the latter. The spring elements may adjoin the spring sleeve in actuating direction in the form of radially inwardly bent strips. The inside diameter defined by the free ends of said inwardly bent strips is accordingly smaller than the inside diameter of the hollow-cylindrical spring sleeve.
The receiving sleeve may be provided at its end facing the brake pedal with a funnel-shaped widening of its inside diameter. Such a refinement of the end of the receiving sleeve facing the brake pedal guarantees that the detent connection between actuating rod and input element may be easily established even in the event of the actuating rod being disposed off-center when the actuating rod is introduced into the receiving sleeve.
The funnel-shaped widening of the inside diameter of the receiving sleeve may be realized, for example, by fastening a funnel-shaped component to the brake pedal-side end of the receiving sleeve. The receiving sleeve may have radially at the outside a peripherally extending groove, into which a peripherally extending rib disposed radially at the inside of the funnel-shaped component may be latchingly introduced in order to fasten the funnel-shaped component. Conversely, the receiving sleeve may be provided radially at the outside with a rib and the funnel-shaped component may be provided radially at the inside with a corresponding groove.
According to a preferred embodiment of the invention, an actuating element, which is disposed e.g. in relation to the actuating rod radially at the outside and is movable axially relative to the actuating rod, is provided for actuating the at least one spring element. By means of the actuating element each spring element of the spring sleeve may be swivelled radially outwards in order thereby to release the coupling, occasioned by the spring elements, of the actuating rod counter to actuating direction to the input element.
The actuating element may comprise a portion, which extends into the spring sleeve and cooperates with the at least one spring element. The actuating element may moreover be provided radially at the outside with a step, which cooperates with an end face of the receiving sleeve facing the step in order to limit the axial mobility of the actuating element. The actuating element preferably takes the form of a sleeve guided on the actuating rod and may be coupled by means of a screw-type connection to the actuating rod. The screw-type connection allows an axial relative motion between actuating element and actuating rod.